Cmd prompt changed

I'm currently running windows 7 home premium, 64 bit. A few days ago, I hopped into my cmd prompt to find that instead of the usual "Microsoft windows 7 [version 6.1 etc etc]" copyright notice, it just says "you lose".

I'm guessing this is a prank one of my mates pulled, but I can't figure out how he did it. I can't find any new software installed on the system and it's definitely the original windows cmd prompt.

I know that a simple system restore would probably fix it, but I'm still curious about how they could have done it....but none of my mates will admit to doing it and after 3 days of searching google and checking any method I could think of, I still can't find a way.